Can you answer 6 questions for Adv. Exercise Phys grad class (topic is neuromuscular control)

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EXNS 6203

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Neuromuscular Control 1 Motor Units The motor unit consists of the anterior motor neuron and the specific muscle fibers it innervates  Each muscle fiber generally receives input from only one neuron  Yet a motor neuron may innervate many muscle fibers The number of muscle fibers per motor neuron generally relates to a muscle’s particular movement function  Muscles that require less precision may have several hundred fibers served by one motor neuron.  Muscles that function with great precision may have as few as one muscle fiber per motor neuron. Fig. 19.7. McArdle et al. 2015. Exercise Physiology… LWW All‐or‐None Principle A stimulus strong enough to trigger an action potential in the motor neuron activates all of the accompanying muscle fibers in the motor unit to contract synchronously  There is no such thing as a motor neuron stimulus that causes only some of the fibers to contract. A motor unit does not exert a force gradation; either the impulse elicits an action or it does not  Similarly, a stronger action potential cannot produce a stronger contraction. Fig. 19.7. McArdle et al. 2015. Exercise Physiology… LWW Summation of Force Normal body movements are not made up of simple twitches, but sustained contractions. ↑frequency of stimuli increases > fibers do not have time to relax > “summation” and ↑ force production Fig. 1.12,13. Kenney et al. 2012. Physiology of Sport… Hum.Kin. Gradation of Force (Acute) Amount of force generated in a single muscle fiber is dependent upon the # of crossbridges Force generation of a group of muscles depends on four factors: 1) Number of motor units recruited • A muscle generates considerable force when activated by all of its motor units 2) Frequency of motor unit discharge • Repetitive stimuli that reach a muscle before it relaxes increases the total tension 3) Type of motor unit recruited • Larger / Type II motor units will generate greater force 4) Preloading the muscle (activating the stretch reflex) Types of Muscle Action Tab. 18.1. Plowman et al. 2014. Exercise Physiology… LWW Force‐Velocity Curve Fig. 1.14. Kenney et al. 2012. Physiology of Sport… Hum.Kin. Force‐Velocity Curve Fig. 1.14. Kenney et al. 2012. Physiology of Sport… Hum.Kin. Figure & Notes References McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2014. Kenney, Wilmore, Costill. Physiology of Sport and Exercise (5th ed). Human Kinetics, 2011. Plowman SA & Smith DL. Exercise Physiology for Health, Fitness, & Performance (4th ed). Lippincott Williams & Wilkins, 2014 Motor Unit Types 1 Motor Unit Characteristics A motor unit contains only one specific muscle fiber type (type I or type II) or a subdivision of the type II fiber with the same metabolic profile Motor units are classified based on three physiologic and mechanical properties of the muscle fibers they innervate: Twitch characteristics Tension characteristics Fatigability 2 Twitch Characteristics Major characteristics for common motor unit categories: Fast twitch, high force, and fast fatigue (type IIx) Fast twitch, moderate force, and fatigue resistant (type IIa) Slow twitch, low force, and fatigue resistant (type I) Motor neurons have a stimulating effect on the muscle fibers they innervate in a way that modulates the fibers’ properties and adaptive response to stimuli 3 Motor Unit Characteristics Type IIx Fig. 19.11. McArdle et al. 2010. Exercise Physiology… LWW Type IIa Type I 4 Motor Unit Characteristics >300 Tab. 1.1,2. Kenney et al. 2012. Physiology of Sport… Hum.Kin. 5 Size Principle Low‐threshold motor units are recruited first and have lower force capabilities than higher‐threshold motor units. Typically, to get to the high‐ threshold motor units, the body must first recruit the lower‐threshold motor units. Fig. 5.2. Baechle et al. 2009. Essentials of Strength… Human Kinetics 6 Size Principle This orderly recruitment of specific motor units to produce a smooth muscle action allows the CNS to fine tune skeletal muscle activity to meet demands of the motor task. Exceptions exist, especially with respect to explosive, ballistic contractions that can selectively recruit high‐ threshold units to rapidly achieve more force and power. (Selective recruitment) Fig. 19.12. McArdle et al. 2015. Exercise 7 Physiology… LWW Figure & Notes References McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2014. Baechle & Earle. Essentials of Strength & Conditioning, 3rd Editiion. Human Kinetics, 2009. Kenney, Wilmore, Costill. Physiology of Sport and Exercise (5th ed). Human Kinetics, 2011. 8 Proprioceptors 1 Proprioceptors Sensory receptors in the muscles and tendons that are sensitive to stretch, tension, and pressure  Ex. Muscles spindles and golgi tendon organ Almost instantaneously relay information about muscular dynamics and limb movement to conscious and subconscious portions of the CNS Allows continual monitoring of the progress of any sequence of movements and serves to modify subsequent motor behavior  Important for powerful, complex coordinated movements  Can enhance muscle relaxation https://www.youtube.com/watch?v=7T4NI_2qDEM 2 Muscle Spindles Provide mechano‐sensory information about changes in muscle fiber length and tension Primarily respond to any stretch of a muscle and initiate a stronger muscle action to counteract this stretch Important to utilize for powerful contractions Important to minimize when relaxing a muscle Fig. 19.13. McArdle et al. 2010. Exercise Physiology… LWW 3 Neurophysiological Model of Stretch Reflex Activation of muscle spindles initiates a stretch reflex  Known as “pre‐loading” the muscle Three main components:  Muscle spindle that responds to stretch  Afferent nerve fiber that carries the sensory impulse from the spindle to the spinal cord  Efferent spinal cord motor neuron that activates the stretched muscle fibers Ex. patellar reflex Fig. 19.14. McArdle et al. 2010. Exercise Physiology… LWW 4 Mechanical Model of Stretch Reflex Elastic energy in tendons and muscles is increased with a rapid stretch (eccentric muscle action) and then briefly stored. If a concentric muscle action follows immediately, the stored energy is released, contributing to the total force production. If a concentric muscle action does not occur immediately following the eccentric action, then the stored energy dissipates and is lost as heat. 5 Plyometric Mechanics and the Stretch Shortening Cycle The stretch‐shortening cycle (SSC) combines mechanical and neurophysiological mechanisms and is the basis of plyometric exercise. A rapid eccentric muscle action stimulates the stretch reflex and storage of elastic energy, which increase the force produced during the subsequent concentric action. Table 16.1. Baechle et al. 2009. Essentials of Strength… Human Kinetics 6 Flexibility and Stretch Reflex Proprioceptors and Stretching    Static Dynamic Ballistic • Fig. 13.7. Baechle et al. 2009. Essentials of Strength… Human Kinetics A stretch reflex occurs when muscle spindles are stimulated during a rapid stretching movement. •Limits muscle relaxation  Proprioceptive Neuromuscular Facilitation (PNF) Stretching 7 Golgi Tendon Organs Connect to extrafusal fibers near tendon’s junction to muscle Detect differences in the tension generated by active muscle to protect the muscle and surrounding connective tissue harness from injury from sudden or excessive load  GTO activation directly related to load applied When stimulated, Golgi receptors transmit signals to the spinal cord to elicit reflex inhibition of the muscles they supply Fig. 19.15. McArdle et al. 2010. Exercise Physiology… LWW 8 GTO Inhibition & Stretching Proprioceptors and Stretching Fig. 13.7. Baechle et al. 2009. Essentials of Strength… Human Kinetics  Proprioceptive Neuromuscular Facilitation (PNF) Stretching •Autogenic inhibition is accomplished via active contraction before a passive stretch of the same muscle. •Reciprocal inhibition is accomplished by contracting the muscle opposing the muscle that is being passively stretched. •Both result from stimulation of Golgi tendon organs, which cause reflexive muscle relaxation. 9 PNF Hamstring Stretches Hold‐Relax (“Push & hold”)  Passive prestretch (10 seconds), isometric hold (6 seconds), passive stretch (30 seconds) https://www.youtube.com/watch?v=gvOQK8qNi9E Fig. 13.1,2. Baechle et al. 2009. Essentials of Strength… Human Kinetics 10 PNF Hamstring Stretches Hold‐Relax (“Push & hold”)  Passive prestretch (10 seconds), isometric hold (6 seconds), passive stretch (30 seconds) Contract‐Relax (“Move”)  Passive prestretch (10 seconds), concentric muscle action through full ROM, passive stretch (30 seconds) https://www.youtube.com/watch?v=gvOQK8qNi9E Fig. 13.1,2. Baechle et al. 2009. Essentials of Strength… Human Kinetics 11 PNF Hamstring Stretches Hold‐Relax With Agonist Contraction (“Push, then Pull”)  During third phase (passive stretch), concentric action of the agonist used to increase the stretch force Fig. 13.10,11. Baechle et al. 2009. Essentials of Strength… Human Kinetics 12 Figure & Notes References McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2014. Baechle & Earle. Essentials of Strength & Conditioning, 3rd Editiion. Human Kinetics, 2009. 13 EXNS 6203 – Guided Study Worksheet Name: Week 11 – Neuromuscular Control 1) Explain how the All or None Principle dictates that individual muscle fibers cannot exert a gradation of force. Then explain how muscle groups are able exert a gradation of force. 2) Explain the force-velocity curve and how it applies to exercise training. 3) Compare and contrast Type 1 and Type 2 motor units. Use the Size Principle in part of your explanation. 4) Distinguish between the influence of muscle spindles and golgi tendon organs on muscle contraction. 5) Explain the sequence of events involved in preloading a muscle. What is the purpose of preloading? How does plyometric training improve your stretch reflex? 6) Describe the role of the GTOs in PNF stretching.
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Running head: NEUROMUSCULAR CONTROL

Neuromuscular Control
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NEUROMUSCULAR CONTROL

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Neuromuscular Control

Explain how the All or None Principle dictates that individual muscle fibers cannot exert a
gradation of force. Then explain how muscle groups are able to exert a gradation of force.
The principle of the all-or-none law which indicates that the strength of response of a
given muscle fiber or nerve cell is independent upon the stimulus’ strength. In this case, a single
muscle fiber is unable to exert a gradation force because their specific stimulus is above its
threshold; therefore, the muscle fiber or nerve will fire or fail altogether. Essentially, the
individual muscle fibers will also be unable to exert gradation force since they will be unable to
respond.
However, it is possible for muscle groups to exert gradation as a result of specific reasons
underlying in the nature of the muscles when they are in groups rather than occurring
individually. Muscle groups have tension-generating capabilities that are unique when compared
to individual muscles. This feature of muscle groups influences the output of the force which
significantly exerts force gradation. The activation of these muscles randomly produces a linear
force which increases with progressive recruitment while activation in increasing force results to
the production of exponential force.
Explain the force-velocity curve and how it applies to exercise training.
The conception of the force-velocity curve is primarily viewed as a physical depiction of
the inverse correlation between velocity and force. A basic understanding of the force-v...


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